The 100mm IS L lens is the best for using autofocus on bugs moving around, but in my experience this works best with a body with really nice autofocus such as 1D-X. For general macro shooting your best bet is the 180mm macro, because it allows greater distance from the subject and it allows using an extender such as the 1.4x or 2x extenders, which work with this lens (I often use the 2x extender). Working distance is an important issue, because with the 100mm lens I usually take the lens hood off, so that I won't get too close to an insect, which might either fly or crawl away. I don't tend to shock freeze macro subjects, before I take shots
Before I forget to mention it: You should add a focusing rail to your tripod, adding one piece to the gear M.ST listed. A focusing rail will allow you to set your lens to minimal distance and then you use the focusing rail to focus.